import java.util.Scanner;
//求斐波那契数列的范围和
//这道题有几个坑，第一个是要用大数表示，32位的数表示不了，第二个是from和to可以是一样的
//如果两者一样，输出就是相应斐波那契数列的值
class Fibonacci {
	Fibonacci(int from, int to) {
		len = to;
		num = new long[len];
		num[0] = 1;
		if (len > 1)
			num[1] = 1;
		sum = 0;
		setFib(from);
	}
	private void setFib(int from) {
		for(int i = 2; i < len; i++) {
			num[i] = num[i - 1] + num[i - 2];
		}
		sum = num[from - 1];
		for(int i = from; i < len; i++)
			sum += num[i];
	}
	public long getFib(){
		return sum;
	}
	private int len;
	private long[] num;
	private long sum;
}


public class Main {
	public static void main(String[] args) {
		Scanner cin = new Scanner(System.in);
		while (cin.hasNext()) {
			Fibonacci fib = new Fibonacci(cin.nextInt(), cin.nextInt());
			System.out.println(fib.getFib());
		}
		cin.close();
	}
}